A display device may include a light guide, such as an optical wedge, that transmits an image to a display surface, focuses an image on a detector, or does both. Light may propagate between light input/output interfaces in the light guide via total internal reflection. Depending on the application, certain optical features, such as Fresnel lens features, may also be provided in the light guide. A high degree of smoothness and dimensional fidelity may be desired for these features. However, producing such light guides with a reproducibly high level of dimensional fidelity may be pose challenges.
One possible method of forming a light guide is injection molding. Injection molding generally involves injecting molten plastic into a mold, and then allowing the plastic to cool and solidify. However, many plastics shrink while cooling. Therefore, it may be challenging to manufacture parts of a precise thickness via injection molding. Further, because the magnitude of shrinkage is dependent upon the thickness of the plastic, various portions of a non-uniform plastic part, such as a wedge-shaped light guide, may shrink at different rates, thereby compounding the difficulties in molding precision parts via injection molding.